Clean up algorithm to be more user-friendly

At the core, the lick detector is using a change-detection algorithm to detect licks.

This are many well-documented ways of doing this ([PDF](https://isy.gitlab-pages.liu.se/fs/en/courses/TSFS06/PDFs/Basseville.pdf)). And while the Lick Detector scheme is basically the CUSUM algorithm, it's not obvious. Let's make some algorithm tweaks to make the code more familiar to people with a CUSUM background.